Traditional methods of making an optical surface profile involve grinding and polishing. Automated polishing typically uses a turn table, which is ideal for spherically symmetric surfaces, but it can destroy small wavefront profiles.
Wavefront profiles typically comprise peaks and valleys of the order of microns as measured in optical path difference (OPD). Even if the profile can be accurately produced on an optical surface, a conventional polishing process removes up to a couple of microns of material and it will tend to erase most if not all the intended profile distribution as if they are part of the irregularity to be polished off.
With the advent of a diamond turning CNC machine, 4 and 5 axis free-form precision cutting became commercially available. Multi-axis polishing has also been developed. A disadvantage of ultra high precision CNC is its high cost.
It is desirable to provide a method of making high precision optical surfaces, including those with a high order wavefront profile, at a cost effective level.